Field of the Disclosure
The present disclosure relates to a through wiring substrate, a device having the through wiring substrate, and a method for manufacturing the substrate and the device.
Description of the Related Art
With the decrease in size and the increase in the functionality including the processing speed and versatility, a through wiring is used to enable, at the shortest distance, electrical connection between chins constituting a device or between elements on the substrate front surface and electrode pads on the substrate rear surface. For example, after forming through holes which penetrate through a substrate, the through holes are filled with a conductive material. Then, element electrodes on the front surface side of the substrate are electrically connected with electrode pads on the rear surface side of the substrate via through wirings formed of the conductive material. Methods for filling through holes with a conductive material include the electroplating method. With a high aspect ratio of through holes, bottom-up electroplating in which a seed layer is formed at one ends of through holes is effective to obtain reliable through wirings. Generally after plating, the conductive material protruding from both ends of the through holes is polished to be planarized so that both end faces of the conductive material become as high as the substrate surfaces. The conductive material planarized in this way serves as through wirings.
The plated conductive material has uneven protruding height and uneven polishing. Therefore, for all through holes, it is necessary to concave the end faces of the through wirings from the substrate surfaces to remove protruding portions of the conductive material. The larger the protruding height of the conductive material, the longer the polishing time and the larger the uneven polishing. The larger the uneven plating and uneven polishing, the larger the number of through wirings having end faces largely concaved from the substrate surfaces, i.e., the larger the number of through wirings with a large depth of the positions of the end faces from the substrate surfaces.
Further, at the time of polishing, end faces of the conductive material are plastically deformed by mechanical stress, possibly causing gaps between the through wirings and the inner walls of the through holes. The larger the amount of polishing, the larger the gaps. Meanwhile, a large depth of the end faces of the through wirings or a large gap between the through wirings and the through holes is likely to cause the following problems when forming elements on a substrate having through wirings:    (1) in the vicinity of through wirings, the uniformity in film thickness of a thin film configuring elements degrades and the membrane stress distribution on the thin film increases. Therefore, variations in the element characteristics are likely to increase. To decrease variations the element characteristics, it is possible to avoid arranging elements in the vicinity of through wirings. In this case, however, the integration degree of elements will decrease.    (2) At end faces of through wirings, electrical connection with element electrodes or electrode pads may possibly be degraded.    (3) Large unevenness on the substrate surfaces makes it difficult to manufacture minute patterns.
Japanese Patent Application Laid-Open No. 2008-135482 discusses a technique for reducing a gap arising between a through wiring and the inner wall of a through hole due to polishing. In the technique discussed in Japanese Patent Application Laid-Open No. 2008-135482, both end faces of a main portion of a through wiring is provided with contact portions formed of a conductive material having a higher elastic modulus than the main portion. Accordingly, at the time of polishing, since the conductive material having a high elastic modulus provides small plastic deformation, a gap hardly arises between the through wiring and the inner wall of the through hole.
However, in the technique discussed in Japanese Patent Application Laid-Open No. 2008-135482, it is necessary to perform plating three times by using different materials to form the main portion of the through wiring and the contact portions at both end faces of the main portion, resulting in complicated manufacturing processes. Further, since the main portion and the contact portions of the through wiring are formed of different materials, a contraption for mutual adhesiveness may be required.